Dysphagia is a medical term given to an inability to swallow or an inability to swallow in a safely controlled way. It has been reported that 7%-10% of all adults older than 50 years of age present with clinically significant dysphagia. Of those over the age of 60, this increases to 14% of the entire adult population. In total 10 million Americans are evaluated each year in clinics and hospitals for swallowing difficulties. It has also been reported that >51% of institutionalised elderly patients present with oropharyngeal dysphagia.
Collectively these figures reflect the fact that neurogenic dysphagia (dysphagia arising from neurological damage) can develop due to a very wide range of underlying conditions such as traumatic brain injury, cerebral palsy, head and neck cancer and neurodegenerative diseases like MS, Parkinson's and Alzheimer's. It is however stroke that is probably the most recognized single cause of dysphagia—greater than 50% of patients who have a stroke will present with dysphagia.
Complications that have been associated with dysphagia post-stroke include pneumonia, malnutrition, dehydration, poorer long-term outcome, increased length of hospital stay, increased rehabilitation time and the need for long-term care assistance, increased mortality, and increased health care costs. These complications impact the physical and social well being of patients, quality of life of both patients and caregivers, and the utilization of health care resources.
Dysphagia can be difficult to diagnose and to monitor. Symptoms may improve or worsen over even short periods of time. Gold standard diagnostic methods for swallowing assessment involve the use of instrumental exams that visualise the movement of materials from the oral spaces to the oesophagus. Examples of such methods include videofluoroscopy (VFS) and Fibroscopic Endoscopic Evaluation of Swallowing (FEES). These allow quantification of the time involved in the movement of a bolus of material through the oral spaces, the amount of swallowed material that pools in the pharynx and the amount of material that enters into the airways. They can also capture the response of the patient to material entering into the airways as a determinant of level of awareness the patient has to this risk associated event and their ability to respond to it. These methods can be difficult or traumatic for the patient and require substantial expertise and training.
Other diagnostic methods include bedside assessments such as the Toronto Bedside Swallow Test (TORBST). These are observational methods that test the ability of the subject to swallow a variety of different materials. These methods are more qualitative in nature and are designed to screen for the presence or absence of a normal swallow. Whilst they have the advantage of being easy to carry out they lack the diagnostic sensitivity of instrumental methods and in particular are poor at identifying so called silent aspirators whose sensory processes are so compromised they do not react to even substantial amounts of material entering the airways.
The pharyngeal phase of swallowing is initiated voluntarily. This first requires input and oversight from the parts of the brain involved in motor planning. These higher centres receive information about the nature of the material, size of the bolus etc., and modulate the involuntary sequences that will follow. The duration and intensity of muscle contraction can be modified to accommodate a larger bolus for example. Only when the food or liquid bolus is voluntarily pushed through the faucial pillars (the structures to the left and right of the uvula), or in older individuals, when the food is in contact with the base of the tongue, is the reflexive involuntary component of the pharyngeal swallow triggered. This is where the central pattern generator within the medulla (brain stem), modulated by the higher centres comes into play. The reflexive sequence that follows has two key functions: i) controlled passage of food or secretions from the pharynx to the oesophagus; and ii) airway protection.
A common manifestation in neurogenic dysphagia is that whilst the pattern generating processes that control the sequence of activities in swallowing (located in the brain stem) may be intact, the triggers to begin or modulate the swallowing processes are absent or compromised. This can reflect the fact that the sensory input provided by the bolus of material at the back of the throat or base of the tongue is no longer sufficient to be detected and to trigger the reflexive swallowing process. In effect the sensory threshold for that individual has been raised. Whilst the consequences of this increase in sensory threshold may be seen with existing diagnostic methods, the increase and absolute level of the threshold is not measured by these methods.
Pharyngeal Electrical Stimulation (PES) is a method for treating neurogenic dysphagia. It involves the application of electrical stimulation to the pharyngeal mucosa and this results in an increase in activity in the motor cortex and other areas of the brain. These changes facilitate a functional reorganisation of the centres in the brain responsible for controlling and coordinating swallow function.